Electron Paramagnetic Resonance (EPR) spectroscopy is being evaluated for use as a potential screening technique for early detection of cancer. EPR spin labeling techniques are being utilized to elucidate possible membrane and intracellular viscosity changes which may occur in blood components of humans with cancer. A double-blind study will be continued on the EPR signal intensity of Cu plus 2 bound to ceruloplasmin (Cu plus 2-CP) and on the ration Cu plus 2/total Cu in serum samples from female volunteers who are asymptomatic but have a higher than average risk of developing breast cancer. Animal tumor model systems already developed will be utilized to provide lymphocytes for spin labeling studies to determine possible changes in membrane fluidity or cytoplasmic viscosity associated with cancer. These tumor models will also be studied to learn how early after tumor cell implant the changes occur in Cu plus 2-CP level and in the ratio Cu plus 2/total Cu, and to obtain more information on possible hypotheses for these changes. Studies on the molecular properties of CP, including single crystals of CP, will be continued. These will include electron spin echo studies which may help to characterize the binding sites of Cu in the molecule.